It is frequently necessary to selectively connect a driving shaft to a driven shaft to drive the driven shaft. While various coupling devices are available to connect a driving shaft to a driven shaft, such devices have generally been unable to connect a driving shaft to a driven shaft so as to maintain a prescribed relative rotational position between the driving and driven shafts so as to maintain synchronization therebetween. This has been especially true in the poultry processing industry where the entire processing operation is controlled by the overhead conveyor which successively moves the poultry carrying shackles through the plant. Many times the overhead conveyor actually drives the processing equipment through an idler drive unit driven by the conveyor. Because of the required synchronization between the operation of the processing equipment and the overhead conveyor, this equipment has normally been permanently and drivingly connected to the overhead conveyor. Thus, when the processing equipment was not being used, it could not be disconnected which resulted in excessive wear and other damage to the equipment.